Currently, most digital cameras use a zoom lens and a single color image sensor to capture still and video images. The captured images are then digitally processed to produce digital image files, which are stored in a digital memory in the camera. The digital image files can then be transferred to a computer, displayed, and shared via the Internet. The digital camera can also be included as part of a mobile telephone, to form a so-called “camera phone.” The camera phone can transmit the digital image files to another camera phone, or to service providers, via a mobile telephone network.
Small camera size and a large zoom range are two very important features of digital cameras. Users prefer to have a zoom function to provide a more flexible photographic capability. The zoom range is typically composed of both optical zoom which is provided by variable focal length lenses and digital zoom which is provided by a magnification of the digital image after capture. Variable focal length lenses for large zoom range are expensive and generally increase the overall size of the digital camera. Thus, there are trade-offs between small camera size, large zoom range, and low camera cost which must be made when designing a digital camera. With higher cost cameras, such as single lens reflex cameras, these problems are sometimes addressed by using multiple interchangeable zoom lenses, such as two 3:1 zoom lenses, e.g., a 28-70 mm zoom and a 70-210 zoom. This arrangement has user inconvenience shortcomings and higher cost, as well as design complexity issues that make it unsuitable for low cost digital cameras.
Digital zoom based on increased magnification of the image with a corresponding decrease in resolution is well known in the art. Although digital zoom is very fast and simple, the decrease in resolution can produce a perceived decrease in image quality.
In U.S. Pat. No. 5,657,402, a method is described in which a plurality of digital images is combined to form an image. U.S. Pat. No. 5,657,402 addresses the use of multiple images captured at different focal lengths or different times wherein “the plurality of images of various focal lengths, such as a zoom video sequence” (col. 1 lines 21-22) are captured from the same lens. However, U.S. Pat. No. 5,657,402 does not include methods for enabling different fields of view to be captured. In addition, the images captured in U.S. Pat. No. 5,657,402 all include the same number of pixels so that the total exposure time, as well as the storage and readout time, are increased with multiple images.
In U.S. Patent Application 2002/0075258, a panoramic camera system is described in which a moveable telephoto camera is additionally used to capture a high resolution portion of the scene which is then overlaid onto the panoramic image. U.S. Patent Application 2002/0075258 describes the use of a moveable telephoto camera to enable a higher resolution of a portion of the image, wherein the moveable telephoto camera can be moved to the region of the panoramic image where the higher resolution is desired. However, U.S. Patent Application 2002/0075258 uses images of different focal lengths and the image produced has areas of different resolution.
In U.S. Pat. No. 5,717,512, a system for capturing images with different fields of view is described. The system is based on a rotatable and tiltable lens system driven by motors for capturing images of people at an Automatic Teller Machine. The system is large and complex as shown in FIG. 1, and as such is unsuited for use in a compact camera system. The system as described in U.S. Pat. No. 5,717,512 includes three mirrors, a pan and tilt mirror 34, and two folding mirrors 58 and 59 to redirect the light collected from the scene by the pan and tilt mirror to the camera 60. The system also includes three drive motors. The pan and tilt mirror is held in a frame 31 which can be rotated about the optical axis of the imaging lens 36 by pan drive motor 52. The pan drive motor 52 is mounted in pivot plate 53 which is rotatably attached to mounting plate 43. The pan and tilt mirror 34 can also be tilted by the tilt drive motor 44 which is attached to the pan and tilt mirror 34 by linkage 33. The tilt drive motor 44 is attached to pivot plate 53 so that it rotates with pan motions. Focusing of the image onto the camera is done by moving the imaging lens along the optical axis by focus motor 38 and along guide rods 39.
In U.S. Patent Application 2007/0081081, a camera system is mounted on a rotating pivot for capturing overlapping images for a panoramic image. A sensor is included which indicates when each of the multiple images should be captured for good overlap.
No prior art system provides a sufficiently compact, low cost, optical system with a large zoom range for a small, lightweight and relatively inexpensive consumer digital camera. It is additionally desirable to retain good image quality while avoiding substantial increases in the file size associated with a multiple image capture based process while still enabling a large zoom range.